U.S. patent application number 11/570034 was filed with the patent office on 2007-12-27 for rear projection screen and associated display system.
This patent application is currently assigned to Microsharp Corporation Limited. Invention is credited to Iman Ibrahim Khandaker, Yongmin Lee, Samir Mezouari, Anna Taylor O'Neil.
Application Number | 20070296920 11/570034 |
Document ID | / |
Family ID | 32696775 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070296920 |
Kind Code |
A1 |
Mezouari; Samir ; et
al. |
December 27, 2007 |
Rear Projection Screen and Associated Display System
Abstract
A rear projection display method and system, for displaying an
image. The system comprises projection means (18L, 18R) to project
first and second stereoscopic image components; a first
light-redirecting panel (20R) and a second downstream
light-redirecting panel (20L) to receive light representative of
the first and second image components, respectively, from the
projection means and to redirect that light substantially in a
downstream direction, the first and second panels arranged to
spatially multiplex the first and second image components; and a
parallax optic element (22) located downstream of the second panel
to provide at a downstream viewing zone (24) the first and second
image components for autostereoscopic viewing of the image. The
projection means may be switchable between 2D and 3D viewing modes.
A 3D image may be produced by simultaneously or sequentially
projecting a series of 2D image sections, using diffuser elements
(45). A method of displaying a 3D image is also disclosed.
Inventors: |
Mezouari; Samir; (Brentwood,
GB) ; O'Neil; Anna Taylor; (Milton Keynes, GB)
; Lee; Yongmin; (Suwon, KR) ; Khandaker; Iman
Ibrahim; (Watford, GB) |
Correspondence
Address: |
WORKMAN NYDEGGER
60 EAST SOUTH TEMPLE
1000 EAGLE GATE TOWER
SALT LAKE CITY
UT
84111
US
|
Assignee: |
Microsharp Corporation
Limited
52 Shrivenham Hundred Business Park, Majors Road
Watchfield
GB
SN6 8TY
|
Family ID: |
32696775 |
Appl. No.: |
11/570034 |
Filed: |
June 7, 2005 |
PCT Filed: |
June 7, 2005 |
PCT NO: |
PCT/GB05/02218 |
371 Date: |
June 20, 2007 |
Current U.S.
Class: |
353/7 ;
348/E13.029; 348/E13.03; 348/E13.042; 348/E13.057 |
Current CPC
Class: |
H04N 13/305 20180501;
H04N 13/346 20180501; H04N 13/363 20180501; H04N 13/395 20180501;
H04N 13/359 20180501; H04N 13/31 20180501; H04N 13/312
20180501 |
Class at
Publication: |
353/007 |
International
Class: |
G03B 21/00 20060101
G03B021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2004 |
GB |
0412651.2 |
Claims
1. A rear projection display system, for displaying an image, the
system comprising: projection means arranged to project first and
second stereoscopic image components; a first light-redirecting
panel arranged to receive light representative of the first
stereoscopic image component from the projection means and to
redirect that light substantially in a downstream direction; a
second light-redirecting panel downstream of the first panel, and
arranged to receive light representative of the second stereoscopic
image component from the projection means and to redirect that
light substantially in the downstream direction, the first and
second light-redirecting panels being arranged so as to spatially
multiplex the first and second image components; and a parallax
optic element located downstream of the second panel and arranged
to provide at a downstream viewing zone the first and second image
components for autostereoscopic viewing of the image.
2. The display system of claim 1, wherein the first and second
image components are spatially multiplexed as a plurality of
alternate and separate first and second component portions.
3. The display system of claim 1, wherein the first and second
light-redirecting panels respectively comprise a rear surface on
which is disposed a plurality of elongate ribs, each rib comprising
a first, light-transmitting external face and a second,
light-reflecting internal face, such that light incident on the
first face of a rib generally obliquely with respect to the panel
is transmitted into that rib and reflected at the second face
substantially in the downstream direction.
4. The display system of claim 3, wherein the second, internal face
is arranged at a suitable angle relative to the first, external
face in order to redirect the light in a direction substantially
perpendicular to a front surface of the optical panel.
5. The display system of claim 3, wherein the first plurality of
ribs disposed on the first panel and the second plurality of ribs
disposed on the second panel are spatially offset with respect to
one another, such that respective portions of light redirected from
the first panel do not take the same path as those portions
redirected from the second panel.
6. The display system of claim 5, wherein the second panel further
comprises a plurality of third faces respectively separating
adjacent ribs, such that light redirected from the first panel is
incident upon the third faces.
7. The display system of claim 6, wherein the third faces are
formed substantially perpendicular to the downstream direction, so
that light redirected from the first panel is substantially
transmitted through the second panel.
8. The display system of claim 3, wherein the second, internal face
of each rib has a light-reflecting coating thereon.
9. The display system of claim 3, wherein the first, external face
has an anti-reflection coating thereon.
10. The display system of claim 6, wherein each third face has an
anti-reflection coating thereon.
11. The display system of claim 3, wherein one or both of the first
and second faces may be curved.
12. The display system of claim 1, wherein the projection means
comprises a first image projection means arranged to project the
first stereoscopic image component to the first light-redirecting
panel and a second image projection means arranged to project the
second stereoscopic image component to the second light-redirecting
panel.
13. The display system of claim 12, wherein the first and second
projection means are arranged to project the stereoscopic images to
the first and second panels respectively either from the same side
of the panels, or from opposite sides.
14. The display system of claim 12, wherein the first and second
image projection means comprise: either a single light source or a
plurality of light sources, and either one or more anamorphic
optical elements or a digital signal processing unit, for the
reduction of field distortion of the image.
15. The display system of claim 12, wherein the first and second
image projection means comprise a respective image source, selected
from the group consisting of: a Liquid Crystal Display (LCD), a
Digital Micromirror Device (DMD), a laser-raster scanner, a
Microelectromechanical System (MEMS), a Cathode Ray Tube (CRT), a
single or an array of Light Emitting Diodes (LEDs), an Organic
Light Emitting Diode (OLED), or Grating Light Valve (GLV), a slide,
a film, or the like.
16. The display system of claim 1, wherein the parallax optic
element is selected from the list comprising: a lenticular element,
a parallax barrier element, a diffraction grating, a birefringent
element, a polarising element, and a holographic element.
17. The display system of claim 1, wherein the projection means is
switchable between a first, 3D viewing mode, and a second, 2D
viewing mode in which the projection means is arranged to project
first and second image components which are identical.
18. A rear projection display system, for displaying an image, the
system comprising: a light-redirecting panel; projection means
arranged to project first and second stereoscopic image components
from respective opposing sides of the light-redirecting panel, the
light-redirecting panel being arranged to receive light
representative of the first and second stereoscopic image
components from the projection means, and to redirect that light
substantially in a downstream direction, so as to spatially
multiplex the first and second image components; and a parallax
optic element, located downstream of the light-redirecting panel
and arranged to provide at a downstream viewing zone the first and
second image components for autostereoscopic viewing of the
image.
19. The display system of claim 18, wherein the light-redirecting
panel comprises a rear surface on which is disposed a plurality of
elongate ribs, each rib having opposed, first and second
light-transmitting external faces and opposed, first and second
light-reflecting internal faces, such that light representative of
the first and second stereoscopic images and incident on the
respective first and second transmitting faces generally obliquely
with respect to the panel is transmitted into that rib and
reflected at the first and second reflecting faces substantially in
the downstream direction.
20. A rear projection display system, comprising: at least a first
image projection means, arranged to project a plurality of 2D image
sections representing a 3D image; at least a first
light-redirecting panel, arranged to receive light representative
of the 2D image sections and to redirect that light substantially
in a downstream direction, so as to spatially multiplex each 2D
image section; and a plurality of diffuser elements arranged
downstream of the or each light-redirecting panel to diffuse
respective multiplexed portions of each 2D section, such that the
2D image sections may be viewed downstream of the diffuser elements
as the 3D image.
21. The display system of claim 20, wherein the projection means is
arranged to project the plurality of 2D image sections
sequentially.
22. The display system of claim 20, wherein the projection means is
arranged to project the plurality of 2D image sections
simultaneously.
23. The display system of any of claim 20, wherein the diffuser
elements are arranged such that only one diffuser element occupies
any particular vertical location.
24. The display system of any of claim 20, wherein redirected light
is diffused only once as it passes through the display system.
25. The display system of claim 20, wherein the diffuser elements
are switchable between a diffusive state and a transparent
state.
26. The display system of claim 20, comprising a plurality of
parallel light-redirecting panels and a respective projection means
associated with each panel, each projection means being arranged to
project a respective 2D section of the 3D image according to its
relative position with respect to the other of the projection
means.
27. The display system of claim 26, wherein each of the
light-redirecting panels comprises a respective plurality of
diffuser elements disposed on its downstream surface.
28. The display system of claim 20, comprising a plurality of
parallel light-redirecting panels, and a light-directing means
arranged such that each 2D section is projected over a rear surface
of its respective panel for redirection in the downstream
direction.
29. The display system of claim 28, wherein the light-directing
means comprises a plurality of folding mirror elements respectively
associated with each panel, and a rotating mirror element arranged
sequentially to scan a respective 2D section of the image from the
image projection means onto a respective folding mirror element, so
as to scan the 2D image over the rear surface of the panel.
30. The display system of claim 20, comprising a light-redirecting
panel, and plurality of panel diffusers arranged parallel with one
another and downstream of the light-redirecting panel, each panel
diffuser having a respective plurality of diffuser elements
arranged thereon such that a different 2D section of the image is
diffused by each panel diffuser.
31. The display system of claim 30, wherein the projection means is
arranged to project the 2D image sections onto a rear surface of
the light-redirecting panel simultaneously as a set of compressed
2D image sections.
32. The display system of claim 30, wherein the locations of the
diffuser elements on a first panel diffuser are varied in regular
steps for adjacent panel diffusers.
33. The display system of any of claim 30, wherein the
light-redirecting panel is arranged to be reciprocated, so that the
2D sections are addressed sequentially to the diffuser elements on
each panel diffuser.
34. The display system of claim 20, wherein the diffuser elements
are arranged in a louvred array of stacked diffuser elements.
35. The display system of claim 34, wherein a thickness of the
louvred stacks is in the range of approximately 0.5 cm to 300
cm.
36. The display system of any of claim 20, wherein the 2D sections
are scanned in any of a vertical, horizontal, or up/downstream
direction.
37. The display system of claim 20, wherein the at least one
light-redirecting panel comprises a rear surface on which is
disposed a plurality of elongate ribs, each rib comprising a first,
light-transmitting external face and a second, light-reflecting
internal face, such that light incident on the first face of a rib
generally obliquely with respect to the panel is transmitted into
that rib and reflected at the second face substantially in the
first direction.
38. The display system of claim 37, wherein the second, internal
face is arranged at a suitable angle relative to the first,
external face in order to redirect the light in a direction
substantially perpendicular to a front surface of the optical
panel.
39. The display system of claim 37, wherein the first plurality of
ribs disposed on the first panel and subsequent pluralities of ribs
disposed on the subsequent panels are spatially offset with respect
to one another, such that respective portions of light redirected
from the first panel do not take the same path as those portions
redirected from the subsequent panels.
40. The display system of claim 39, wherein, apart from the
light-transmitting and light-redirecting faces, the rear surfaces
of the subsequent panels comprise a respective plurality of
surfaces substantially perpendicular to the downstream direction,
such that light redirected from the first and subsequent panels is
substantially transmitted through the subsequent panels.
41. The display system of any of claim 37, wherein the second,
internal face of each rib has a light-reflecting coating
thereon.
42. The display system of claim 37, wherein the first, external
face has an anti-reflection coating thereon.
43. The display system of claim 40, wherein each surface has an
anti-reflection coating thereon.
44. The display system of claim 37, wherein one or both of the
first and second faces may be curved.
45. The display system of claim 20, wherein the first and
subsequent projection means are arranged to project the 2D sections
to the first and subsequent panels respectively either from the
same side of the panels, or from opposite sides.
46. The display system of claim 20, wherein the first and/or
subsequent image projection means comprise: either a single light
source or a plurality of light sources, and either one or more
anamorphic optical elements or a digital signal processing unit,
for the reduction of field distortion of the image.
47. The display system of claim 20, wherein the first and
subsequent image projection means comprise a respective image
source, selected from the group consisting of: a Liquid Crystal
Display (LCD), a Digital Micromirror Device (DMD), a laser-raster
scanner, a Microelectromechanical System (MEMS), a Cathode Ray Tube
(CRT), a single or an array of Light Emitting Diodes (LEDs), an
Organic Light Emitting Diode (OLED), or Grating Light Valve (GLV),
a slide, a film, or the like.
48. A method of displaying a 3D image, comprising spatially
multiplexing respective left and right eye stereoscopic images from
an image projection means using first and second light-redirecting
panels, and passing the multiplexed images through a parallax optic
device such that the left and right eye images may be viewed at a
viewing zone with binocular disparity.
49. The method of claim 48, further comprising extending the
viewing zone horizontally and/or vertically by employing diffuser
or lenticular elements within the display.
50-51. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a display system, and more
particularly to an autostereoscopic and a volumetric image display
system for displaying a three-dimensional (3D) image. The present
invention concerns a 3D image projection system that does not
require a viewer to wear goggles or glasses.
[0003] 2. Discussion of Related Art
[0004] As is well known in the art, a 3D image can be obtained by
combining two images, namely a left eye image and a right eye
image, which are then processed through a suitable 3D display
system. 3D display systems can be categorized by the technique used
to channel the left and right images to the appropriate eye: those
which require optical devices close to the viewer's eyes (such as
glasses or goggles) are known as stereoscopic displays, while those
which have the eye-addressing components completely integrated
within the display itself are known as autostereoscopic
displays.
[0005] With autostereoscopic systems, the only exploitable
constraint for addressing the left and right eye respectively is
the fact that the left and right eyes are spatially separated and
so occupy different points in space. The wavefronts forming the 3-D
image may originate from either fixed or gaze-controlled (i.e.,
viewer-tracked) image planes. In both cases, the content of the
left and right image is channeled to the appropriate eye by means
of direction-multiplexing. Compared with stereoscopic techniques,
it is possible to multiplex more than two views at a time. Thus
with autostereoscopic, multi-view systems it is possible to provide
viewing freedom for more than one viewer.
[0006] Flat panel displays based on LCD technology have optical
properties that make them ideally suited for use as
autostereoscopic 3D displays. In particular, they are optically
flat and have precisely positioned pixels, which allows external
optical components to be added in front of or behind the displays.
In this way, low-cost, high-quality, 3D autostereoscopic displays
may be provided.
[0007] The parallax barrier design which uses optical apertures
aligned with columns of LCD pixels is the simplest way to create a
twin-view 3D display. The left and right images are interlaced in
columns on the display and the parallax barrier is positioned so
that left and right image pixels are blocked from view except in
the appropriate viewing regions. Such display systems are disclosed
in U.S. Pat. No. 6,157,424, which uses a secondary LCD to produce
parallax barriers behind an imaging LCD; U.S. Pat. No. 6,055,013,
which uses a parallax barrier design that blocks light, using
strips of a black mask to form a plurality of viewing windows; U.S.
Pat. No. 5,831,765, which employs alternating, vertical striped
transmitting portions and barrier portions, each barrier portion
comprising a reflecting film and a light absorbing film on opposing
sides; and U.S. Pat. No. 6,239,830, in which viewing windows are
steered to track the viewer in three dimensions, by varying the
pitch and aperture of the parallax barriers in real time, although
with limited tracking range and a relatively complex design.
[0008] The design of parallax apertures is very sensitive to
diffraction effects that lead to crosstalk, which therefore
constrains the minimum useful width of apertures compatible with
uniform intensity at the viewing window. Other problems with
parallax barriers include reduced brightness, due to blocking the
light from pixels and reflections from the surface of the parallax
barrier. A wider parallax aperture increases brightness, but
reduces the apparent three-dimensional effect of the display.
Furthermore, while placing the parallax barrier behind the LCD
results in lower crosstalk, placing it in front of the LCD produces
better uniformity.
[0009] Alternatively, lenticular elements may be used. In 3D
displays, these are normally cylindrical lenses with their axes
arranged vertically with respect to a viewer. The cylindrical
lenses direct the diffuse light allowing different pixels to be
redirected to either the left or right image.
[0010] EP-A-0,354,851 uses a lenticular sheet for a 3D display by
combining pixels for left and right eye images, each having a
binocular disparity. The pitch of each lenticular element is set to
be slightly smaller than the repetitive pitch of a pair of pixels.
Detection of changes in viewer position and changing the positions
of the left and right eye image pixels accordingly is also
disclosed.
[0011] U.S. Pat. No. 5,897,184 discloses a backlight for 2D/3D
display, which uses a lightguide and lenticular elements behind an
LCD display to construct a reduced-thickness backlight. The
lightguide is provided with a series of grooves to generate an
initial set of light lines, which are reimaged by the lenticular
element to form a large number of evenly spaced light lines in
front of the lightguide. The display is able to switch
electronically between 2D and 3D illumination modes, using polymer
dispersed liquid crystal (PDLC) as a switching diffuser. However,
this design has higher crosstalk than a parallax barrier system in
the 3D mode.
[0012] Some autostereoscopic displays use polarisation-based
optical elements. For example, in U.S. Pat. No. 6,046,849, a 3D
display is created by a front parallax barrier effect, which is
made using a patterned retarder and an analyser. Micropolarisers
are used to create a switchable 2D/3D display. However, this design
requires very accurate construction of the patterned retarder array
that is placed inside the LCD stack, if parallax problems are to be
avoided.
[0013] A number of research groups have been working towards
adapting the principle of holography to an LCD-based video
electronics environment. For example, U.S. Pat. No. 6,590,680
discloses a technique of producing video-rate 3D images using LCD
holography. However, the spatial resolution of today's LC-panels is
a serious constraint. It is also difficult to store and transmit
the enormous amount of data contained in a hologram. In addition,
there are problems of colour fringing, due to the diffractive
nature of the hologram.
[0014] An alternative means of producing 3D images is provided by
volumetric display systems. In a volumetric display system, the
effective origins of the wavefronts entering the observer's eyes
match with the apparent spatial position of the corresponding image
points. Thus, the fundamental mechanisms of spatial vision are
fully supported. Exemplary volumetric display systems are disclosed
in EP-A-0,928,117 and U.S. Pat. No. 6,554,430, in which image
points are projected to definite loci in a physical volume of space
where they appear either on a real surface, or as 2D image layers
forming a stack of distinct depth planes. The refresh or repeat
rate has to be sufficiently fast to avoid flickering. In some
systems, phosphor persistence allows only a limited number of
planes to be displayed without visible image smear. In volumetric
displays the portrayed objects appear transparent, since the light
energy addressed to points in space cannot be absorbed by
foreground pixels.
[0015] Thus a number of 3D display systems have been developed, but
their application is limited by many factors. These factors include
diffraction problems from parallax apertures, complex fabrication,
crosstalk, and inefficiency due to blocking of light.
[0016] There is a need therefore for an improved 3D display system.
It would be desirable to provide a cost effective 3D display system
that readily interfaces with a conventional 2D display format, with
real-time interactivity, whilst supporting 3D autostereoscopic
visualization. It would also be desirable to provide a rear
projection display system which is switchable between 2D and 3D
autostereoscopic images, with high optical efficiency, in a slim
housing. In addition, it would be desirable to provide an improved
volumetric 3D display system.
SUMMARY OF THE INVENTION
[0017] The present invention aims to address the above and other
objectives by providing an improved rear projection screen and
associated display system.
[0018] According to a first aspect of the present invention, there
is provided a rear projection display system, for displaying an
image, the system comprising: projection means arranged to project
first and second stereoscopic image components; a first
light-redirecting panel arranged to receive light representative of
the first stereoscopic image component from the projection means
and to redirect that light substantially in a downstream direction;
a second light-redirecting panel downstream of the first panel, and
arranged to receive light representative of the second stereoscopic
image component from the projection means and to redirect that
light substantially in the downstream direction, the first and
second light-redirecting panels being arranged so as to spatially
multiplex the first and second image components; and a parallax
optic element located downstream of the second panel and arranged
to provide at a downstream viewing zone the first and second image
components for autostereoscopic viewing of the image.
[0019] Autostereoscopic display systems currently on the market use
a set resolution display and a parallax barrier along one
dimension, which leads to a loss in resolution in the direction in
which parallax is provided and also a loss in luminance/brightness
of around 50%. The display system of the present invention is
easily scalable to large display sizes and does not suffer from the
disadvantages due to loss of brightness or resolution normally
encountered by direct-view parallax barrier LCD display systems. In
fact, it is possible to increase the resolution of the display
system when in 2D mode, as a result of the
interleaving/multiplexing of the left and right images. It is
therefore possible to run the display system of the present
invention in any of three modes: a standard 2D mode, a
double-resolution 2D mode, and the 3D autostereoscopic mode.
[0020] According to a second aspect of the present invention, there
is provided a rear projection display system, comprising: at least
a first image projection means, arranged to project a plurality of
2D image sections representing a 3D image; at least a first
light-redirecting panel, arranged to receive light representative
of the 2D image sections and to redirect that light substantially
in a downstream direction, so as to spatially multiplex each 2D
image section; and a plurality of diffuser elements arranged
downstream of the or each light-redirecting panel to diffuse
respective multiplexed portions of each 2D section, such that the
2D image sections may be viewed downstream of the diffuser elements
as the 3D image.
[0021] This aspect of the present invention provides the advantages
of eliminating the need for a large scale rotating component and
preventing consequent mechanical failure of components. In
addition, there is no need to use layered LCD panels which
typically attenuate a large amount of light.
[0022] According to a third aspect of the present invention, there
is provided a rear projection display system, for displaying an
image, the system comprising: a light-redirecting panel; projection
means arranged to project first and second stereoscopic image
components from respective opposing sides of the light-redirecting
panel, the light-redirecting panel being arranged to receive light
representative of the first and second stereoscopic image
components from the projection means, and to redirect that light
substantially in a downstream direction, so as to spatially
multiplex the first and second image components; and a parallax
optic element, located downstream of the light-redirecting panel
and arranged to provide at a downstream viewing zone the first and
second image components for autostereoscopic viewing of the
image.
[0023] According to a fourth aspect of the present invention, there
is provided a method of displaying a 3D image, comprising spatially
multiplexing respective left and right eye stereoscopic images from
an image projection means using first and second light-redirecting
panels, and passing the multiplexed images through a parallax optic
device such that the left and right eye images may be viewed at a
viewing zone with binocular disparity.
[0024] According to a further aspect of the present invention,
there is provided an autostereoscopic rear projection display
system for displaying a three-dimensional image on a screen,
comprising a left redirecting optical panel and a right redirecting
optical panel. The redirecting optical panels are used to multiplex
and spatially alternate the left eye image and right eye image, to
produce visually distinct image segments containing
three-dimensional information on parallel-disposed elongated
stripes having substantially mutually parallel vertical axes. The
autostereoscopic rear projection display system includes projectors
to produce a right eye image and left eye image. In one embodiment
of the present invention, a parallax optic element is used to
channel the right image to the right eye, and the left image to the
left eye. In addition, a display system is disclosed which is
formed by a plurality of rear projection screens aligned to produce
a 3D volumetric display.
[0025] The present invention also provides the following aspects
and preferred features:
[0026] An autostereoscopic rear projection display system for
displaying a three-dimensional image on a screen, comprising:
[0027] at least one left redirecting optical panel and at least one
right redirecting optical panel, which are used to multiplex and
alternate spatially the left eye image and right eye image to
produce visually distinct image segments containing
three-dimensional information on parallel-disposed elongated
stripes having substantially mutually parallel vertical axes,
[0028] a projection system projecting a left eye image,
[0029] a projection system projecting a right eye image,
[0030] a parallax optic element.
[0031] Preferably, the left redirecting optical panel and the right
redirecting optical panel redirect the said left eye image and said
right eye image formed by said projection system illuminating each
redirecting optical panel, wherein the said redirecting optical
panel comprises:
[0032] a front planar face,
[0033] a back face having a transparent, substantially periodic
structure constituted of a group of transparent facets;
[0034] a transparent first facet substantially perpendicular to the
transmitted said left eye image or said right eye image, and
[0035] a transparent second planar facet adjoining said first
planar facet and substantially parallel to said left eye image or
said right eye image, and
[0036] a transparent third planar facet, which reflects by total
internal reflection the transmitted said left eye image or said
right eye image, adjoining said second planar facet, and
[0037] a fourth planar facet, which is substantially parallel to
the front planar face, adjoining said third planar facet to the
adjacent said first planar facet.
[0038] Preferably, the first facet of is planar, or is curved so as
to focus the light it transmits.
[0039] Preferably, the said transparent third planar facet forms a
suitable angle relative to said second planar facet in order to
reflect the said left eye image or said right eye image so that
they are redirected substantially perpendicular to the said front
planar face.
[0040] Preferably, said projection system projecting a left eye
image and said projection system projecting a right eye image
include:
[0041] a single light source or a plurality of light sources;
and
[0042] anamorphic optical elements or digital signal processing
elements. These elements allow a focused image at all points across
the screen and reduce field distortions, like but not limited to
keystone-type and cornerstone-type distortion of the image.
[0043] Preferably, the image source is selected amongst the group
consisting of Liquid Crystal Display (LCD), a Digital Micromirror
Device (DMD), a laser-raster scanner, a Microelectromechanical
System (MEMS), a Cathode Ray Tube (CRT), a single or an array of
Light Emitting Diodes (LEDs), Organic Light Emitting Diode (OLED),
or Grating Light Valve (GLV), or any other image source known to
those skilled in the art.
[0044] Preferably, said parallax optical element is a lenticular
sheet placed between the viewer and said redirecting optical
panel.
[0045] Alternatively, said parallax optical element is a set of
parallax barriers placed between the viewer and said redirecting
optical panel.
[0046] Preferably, said first facet and said fourth planar facet
are anti-reflection coated.
[0047] Preferably, said third planar facet is coated to enhance the
said total internal reflection effect.
[0048] Preferably, said fourth planar facet is needed for the
combination of said left eye image and said right eye image.
[0049] Preferably, said projection systems are projecting identical
left and right eye images when two-dimensional viewing is
desired.
[0050] Preferably, the left redirecting optical panel and the right
redirecting optical panel redirect the said left eye image and said
right eye image formed by said projection system arranged
illuminating each redirecting optical panel, wherein the said
redirecting optical panel comprises:
[0051] a front planar face,
[0052] a back face having a transparent, substantially periodic
structure constituted of a group of transparent facets;
[0053] a transparent first planar facet substantially perpendicular
to the transmitted said left eye image or said right eye image,
and
[0054] a transparent second planar facet, which reflects by
internal reflection the transmitted said left eye image or said
right eye image, adjoining said first planar facet and said third
planar facet, and
[0055] a third planar facet, which is substantially parallel to the
front planar face, adjoining said second planar facet to the
adjacent said first planar facet.
[0056] Preferably, the said transparent second planar facet forms a
suitable angle relative to said first planar facet in order to
reflect the said left eye image or said right eye image so that
they are redirected substantially perpendicular to the said front
planar face.
[0057] Other preferred features are set out in the description, and
in the dependent claims which are appended hereto. To appreciate
fully this invention, and many of its advantages, the following
description will be extended in the detailed description following
this section.
[0058] The present invention may be put into practice in a number
of ways and some embodiments will now be described, by way of
example only, with reference to the following figures, in
which:
[0059] FIG. 1 shows schematically an embodiment of the present
invention illustrating the multiplexing of left and right
projectors for the formation of a 3D image;
[0060] FIG. 2 shows schematically an arrangement of the two optical
panels forming left and right images, in accordance with one
embodiment;
[0061] FIGS. 3A and 3B show schematically an alternative
arrangement of an optical panel, in accordance with a further
embodiment;
[0062] FIG. 4 shows schematically a further arrangement of the two
optical panels forming left and right images, in accordance with a
still further embodiment;
[0063] FIG. 5 shows an isometric view of an embodiment employing
lenticular elements;
[0064] FIG. 6 shows a schematic plan view of stereo zones;
[0065] FIG. 7 shows schematically a volumetric display employing a
plurality of projectors and aligned screens with diffusing
elements, according to a further embodiment;
[0066] FIG. 8 shows schematically an embodiment of a volumetric
display comprising a plurality of aligned screens with a scanned
array of emitters/modulators;
[0067] FIG. 9 shows schematically an embodiment of a volumetric
display comprising a light-directing panel aligned with diffusing
elements;
[0068] FIG. 10 shows schematically an embodiment of a volumetric
display comprising a reciprocating light-directing panel;
[0069] FIG. 11 shows schematically an embodiment of a volumetric
display comprising a light-directing panel combined with diffusers
arranged in louvred stack; and
[0070] FIG. 12 shows schematically a further embodiment
illustrating the multiplexing of left and right image portions
using a single redirecting panel.
DETAILED DESCRIPTION OF THE INVENTION
[0071] One aspect of the present invention provides a 3D display
system which optically combines a right eye image with a left eye
image to produce a 3D spatially multiplexed image.
[0072] FIG. 1 illustrates one preferred embodiment of a 3D rear
projection display system that includes a left-image projector 18L,
a right-image projector 18R, a right redirecting optical panel 20R,
a left redirecting optical panel 20L, and a lenticular sheet 22.
The right-eye image component generated by the right-image
projector 18R is irradiated to the rear surface of the right
redirecting optical panel 20R. Here, it is redirected towards the
lenticular sheet 22 and a downstream viewing region 24. Thus, in
addition to the optical panel 20R the redirected light also travels
through the optical panel 20L, towards the lenticular sheet 22.
Concurrently, the left-eye image component generated by the
left-image projector 18L is irradiated to the rear surface of and
then redirected by the left redirecting optical panel 20L, in the
downstream direction towards the lenticular sheet 22.
[0073] The left and right redirected light is arranged to remain
distinct upstream of the lenticular sheet 22, i.e. spatially
multiplexed, so the left and right redirected light does not take
the same path to the sheet, as shown in FIG. 1. The left and right
stereoscopic image components are spatially multiplexed as
substantially distinct, alternating left and right image
portions.
[0074] The lenticular sheet 22 serves as a parallax optic element
and brings the multiplexed light to the viewing region 24. Here,
within the viewing region 24, a viewer may view the left and right
stereoscopic components and, due to the effect of binocular
disparity, the viewer sees these separate 2D images as a single 3D
image.
[0075] Of course, while the above embodiment describes the left
light-redirecting panel 20L as being downstream of the right
light-redirecting panel 20R, the order of the panels may be
changed. In this case, it is the redirected light representative of
the left-eye image which passes through the right redirecting panel
20R on its way to the lenticular sheet 22.
[0076] The projectors 18L, 18R used in the described embodiments of
the present invention may comprise any conventional form capable of
projecting a viewing image. One such embodiment of the projector
could entail, for example, the use of anamorphic optical elements
or a digital signal-processing unit for reduction of field
distortion (such as keystone-type, or cornerstone-type, distortion)
of the image, with a suitable light source in each for producing
the right-image and the left-image. This may be beneficial in
reducing the effect resulting from projecting the left- and
right-eye images at an acute angle with respect to the redirecting
panels 20L, 20R. The projectors may be placed at either side or
both sides.
[0077] The light source (not shown) may be a light bulb, slide
projector, video projector, or laser. Some form of light modulator
may also be included in each of the projectors 18L, 18R, to
modulate the right-image and the left-image light. There are many
types of modulator which can be included in different embodiments
of a 3D rear projection display system. For example, the modulator
may comprise, but is not limited to, one or more of the following:
a conventional Liquid Crystal Display (LCD), a Digital Micromirror
Device (DMD), a laser-raster scanner, a Microelectromechanical
System (MEMS), a Cathode Ray Tube (CRT), a single or an array of
Light Emitting Diodes (LEDs), Organic Light Emitting Diode (OLED),
Grating Light Valve (GLV), a slide, a film, or any other image
source known to those skilled in the art.
[0078] The projectors 18L, 18R may also include suitable imaging
optics for distributing the left-image and right-image light
horizontally and vertically over the rear face of each optical
panel, 20L, 20R, for transmission therethrough. The imaging optics,
which may include folding mirrors and/or lenses, are preferably
optically aligned between the back face of each optical panel 20L,
20R and the light modulator.
[0079] In another embodiment, the projectors 18L, 18R could be
situated so as to illuminate the optical panels 20L, 20R from the
same side, instead of from opposite sides as shown in FIG. 1. If
the projector 18L were moved to the same side as the projector 18R,
optical panel 20L would need to be rotated by 180 degrees around an
axis normal to the centre of the optical panel to enable the
apparatus to function as intended. In either case, it is preferable
for the optical panels 20L, 20R to be separated from each other
sufficiently to allow the image from the projector irradiating the
downstream optical panel to cover its full extent. Of course, this
depends on the angle of incidence of the image light on the optical
panels, but it is preferred for the light to impinge upon the
optical panels at an oblique angle.
[0080] FIG. 2 illustrates the process of optically combining
(multiplexing) the left eye image with the right eye image. In this
figure, the rear surface of the optical panels is shown to include
a repeating pattern of elongate ribs, having a characteristic
profile. In this embodiment, each rib is made up of four parts
(although, in general, other embodiments of at least, but not
limited to, three facets are possible): a first part is a
light-transmitting facet 10, which is arranged to be substantially
perpendicular to the direction of incident light on the
transmitting face, so as to maximise light transmission; the second
part is a facet 11 which is generally parallel to the front surface
of the optical panel; the third part is a light-reflecting facet
12, which is arranged to reflect the light which has entered the
rib via facet 10 by means of total internal reflection and/or a
light-reflecting coating on the facet; and the fourth part is a
further facet 13, which is generally parallel to the front surface
and serves to separate adjacent ribs from each other.
[0081] The transparent facet 10 is planar in the preferred
embodiment. The incident rays of image light are arranged to be
substantially perpendicular to the facet 10, which helps to reduce
the formation of ghost images and losses due to Fresnel
reflections. The incident angle and pitch can be chosen
appropriately for optimum multiplexing of the right and left
images. Preferably, the angle of incidence has a value
substantially between 0 and 90 degrees, more preferably the angle
of incidence has a value substantially between 0 and 60 degrees,
most preferably the angle of incidence has a value substantially
between 0 and 30 degrees.
[0082] Facet 11 is planar and generally parallel to the rays of the
incident light. Facet 12 is planar and forms a suitable angle with
facet 11 to reflect the light transmitted by facet 10 towards the
lenticular lens sheet 22. The surface of facet 12 may be coated for
improved reflection. Because the index of refraction of the
environment external of the optical panels 20L, 20R is lower than
the index of refraction of the redirecting optical panels
themselves, facet 12 of the left redirecting panel 20L redirects
the left-image light, and facet 12 of the right redirecting panel
20R redirects the right-image light, by total internal reflection,
depending upon the specific refractive index and angle of incidence
of light.
[0083] In order to maintain the left and right images as distinct
and alternate images, the left and right redirected light cannot be
collinear. Accordingly, the pattern of ribs on one of the optical
panels 20L, 20R is offset with respect to the other (by
approximately half the pitch for the ribs). Thus facet 13 in
optical panel 20L is planar and is perpendicular to the light
leaving optical panel 20R after its redirection. As such, the right
image portions are hardly reflected upon encountering the left
optical panel 20L, so the right-image is transmitted by the left
optical panel. In this way, the light passing downstream of the
left light redirecting panel 20L comprises alternating and
substantially parallel left and right redirected light.
[0084] FIGS. 3A and 3B illustrate schematically an alternative form
for the optical redirecting panel 20. The redirecting panel 20 of
FIGS. 3A and 3B may be used substantially as illustrated for the
upstream of the two optical panels, which may be either the left or
the right light redirecting panel, but which is shown to be the
right redirecting panel 20R in FIGS. 1 and 2. However, as mentioned
above, it is preferable for the second of the redirecting panels
(i.e., the downstream of the two) to include facets on its rear
surface which are parallel to its front surface, so that the light
redirected from the first redirecting panel can be transmitted
through the panel substantially without deviation. In this case,
therefore, facets 11 and 13b are preferably perpendicular to the
light redirected from the first panel (or, in other words, facets
11 and 13b on the second, downstream panel 20 are preferably
parallel to its front surface).
[0085] The panel 20 may be a rigid sheet of transparent glass or
plastics, having a rear surface provided by a plurality of parallel
ribs and grooves, the longitudinal extent of which runs generally
perpendicular to the direction of the light rays passing to the
rear surface of the panel from the image projecting means. More
particularly, the rear surface may have, in section perpendicular
to the planes of major extent of panel 20, and perpendicular to the
longitudinal extent of the ribs and grooves, a profile or waveform,
as shown in FIG. 3A or FIG. 3B, comprising a series of identical or
similar elements each of which may be regarded as defining a
respective rib, or lenticular prism, and an adjoining groove, each
said element comprising a plurality of light segments, defined by
respective faces or facets, (also referred to herein as sections),
of the respective rib or groove. The ribs and grooves of the rear
of panel 20 may be of constant cross-section throughout their
length. In the arrangement shown, the projector 18L or 18R directs
its light from one side onto the back of panel 20 and the ribs and
grooves on the back of the panel run vertically.
[0086] Each rib on the rear surface of the panel 20 may include a
transparent facet 10, which may be planar, or may be curved
convexly to some extent in the preferred embodiment, the facet 10
extending almost perpendicular to the planes of major extent of the
panel 20. More particularly, the facets 10 are substantially
perpendicular to the direction of the incident light rays (see FIG.
3B) of imaging light which strike the rear surface of the panel 20
at a small angle .alpha. with respect to the planes of major extent
of the panel 20. Thus, the rays of image light are substantially
perpendicular to the facet 10, which prevents the existence of
ghost image light.
[0087] Each rib/grove element includes, extending from the rearmost
limit of facet 10, a face or section 11 which is optically
non-functional and extends generally perpendicularly to facet 10
and thus parallel with the incident light rays (at least, for the
first of the light redirecting panels 20; for the second panel,
this facet is preferably parallel with the panel's front surface).
The facet 11 extends to an internally reflective face or section 12
which slopes from facet 11 towards the front surface of the panel
and terminates, in the arrangement of FIGS. 3A and 3B, in the
bottom of a groove, the opposite wall of which is formed by an
optically non-functional face or section 13a extending rearwardly
to a yet further face or section 13a which extends, generally
parallel with the front surface of the panel 20, to the edge
nearest the front surface of panel 20 of the next rib/groove
element. As shown in FIG. 3B, the incident light rays passing into
the panel 20 through the facet 10 of such a rib/groove element are
reflected, internally, i.e. within the panel, at facet 12 of that
rib/groove element, to pass approximately perpendicular to the
planes of major extent of the panel, (and thus approximately
perpendicular to the front surface of the panel), through the panel
20 to exit through said front surface, towards the lenticular sheet
22.
[0088] The material that forms the optical display panel can be
suitably selected to be transparent according to the application.
The curvature of the facets 10 in the preferred embodiments
controls the horizontal viewing angle of the panel display and
concentrates or focuses the transmitted light in the horizontal
direction. The incident angle .alpha. dictates the depth of a
cabinet housing of the display system and in the present embodiment
a has an acute value. Preferably, a has a value between 0 and 90
degrees, more preferably between 0 and 60 degrees, most preferably
between 0 and 30 degrees. As noted, the facet 11 may be planar and
parallel to the rays of the incident light. The facets 12 may also
be convexly curved, for example of conical elliptical, hyperbolic,
or spherical shape, or may be planar. The facets 12 form a suitable
angle with respect to facets 10 to reflect the transmitted light
towards the lenticular sheet 22. The surface of each facet 12 may
have a light reflecting coating for better reflection. The index of
refraction of the environment medium is lower than the index of
refraction of optical display panel 20, and the facets 12 may
redirect the image light by total internal reflection, without the
need for a reflective coating, depending upon the specific
refractive index and angle of incidence of light. The facets 13a
and 13b, which do not intercept the light may have a curved or an
arbitrary shape, but are preferably planar.
[0089] The optical panels 20L, 20R of FIG. 2 may in some
embodiments be replaced with optical panels, known individually in
the prior art, as shown in FIG. 4. Here, each rib comprises three
parts: a transmitting facet, a reflecting facet and a separating
facet.
[0090] In addition, any combination of the various optical
redirecting panels 20 described above may be used together.
[0091] In other embodiments, facets 10 and 12 may be curved, to
enable light focusing while the light passes through the optical
panels 20L, 20R. In still other embodiments, the light-transmitting
facets 10 and 13 may be coated with an anti-reflection coating to
further improve transmission efficiency.
[0092] FIG. 5 shows an isometric view of an embodiment illustrating
the construction of a system creating an autostereoscopic visual
effect with lenticular elements 22. The spatially multiplexed image
formed at the front of the optical panel 20L is selectively imaged
by each of the cylindrical lenses in the lenticular sheet, in such
a way that the right image segments are directed towards the right
eye of a viewer 30, while the left image segments are directed
towards the left eye of the viewer 30. It is preferable for the
pitch of the cylindrical lenses to be approximately twice that of
the left and right multiplexed image portions. In some embodiments,
the pitch of each lenticular element is set to be slightly smaller
than the repetitive pitch of a pair of left and right multiplexed
image portions. The binocular disparity effected by the display
system results in the left and right images viewed by the viewer 30
being interpreted as a single image in three dimensions.
[0093] Instead of the lenticular sheet 22, in some embodiments, it
may be preferable to use a different parallax optic element, such
as a parallax barrier element, diffraction grating, birefringent
element, polarising element, or a holographic element.
[0094] FIG. 6 illustrates a schematic plan view of stereo zones.
The region in which the left and right eyes are located is the
region of greatest left/right-eye image reinforcement, so FIG. 6
shows the optimal position of the viewer 30 for appreciating the 3D
effect. This can be expanded to more than one viewer, as is known
in the art (see, for example, U.S. Pat. No. 6,433,930).
[0095] When a user does not wish to view images in three
dimensions, this capability may be switched off and the display
system will return to 2D display functionality. In this case, the
left and right images produced by the projectors 18L, 18R will
simply be the same, so that, even with the multiplexing of the left
and right images, the image viewed by both eyes will be identical
(i.e., no binocular disparity). The image will therefore appear in
two dimensions.
[0096] FIG. 7 illustrates a further embodiment of the present
invention, namely a volumetric display system comprising a
plurality of projectors 50 and parallel, aligned light-redirecting
panels 40 with diffusing elements 45. As before, each projector 50
is associated with a respective optical redirecting panel 40. Each
optical panel 40 comprises horizontal strips of diffuser 45
situated at the front face of the optical panel 40. Each projector
50 generates a 2D image representative of a slice or section of the
3D image to be displayed corresponding to the position, or depth,
of the projector. In this way, the sequence of the projectors 50
corresponds to increasing/decreasing depth of the 3D image, so the
volumetric 3D image is able to preserve depth information. In
operation, each projector 50 illuminates the back face of its
associated optical panel 40, which directs by internal reflection
the projected image toward the viewer, in a downstream direction,
as before. This may be performed either sequentially for each panel
and projector combination, or simultaneously. In either case, the
diffuser elements 45 on each respective redirecting panel 40
intercept and diffuse the light which is redirected through that
panel's ribs, so that the 2D image section formed by the array of
diffuser elements on the particular panel is registered by a viewer
as emanating from the depth location occupied by the panel.
[0097] The diffuser elements 45 may be formed by structured
diffusers, holographic diffusers, etc., but preferably by
switchable diffusers (such as LCD elements).
[0098] When the 2D image sections are displayed sequentially (which
sequence may be either from panel-to-adjacent panel, or any
repeating pattern which addresses each panel once per cycle), the
diffuser elements 45 are preferably switchable diffusers. Such
switchable diffuser elements then allow a relatively large number
of light redirecting panels 40 to be used, since the problem of the
rearmost viewing cones from the diffuser elements 45 on the first,
upstream panel 40 impinging on subsequent diffusion elements can be
avoided. That is, only the diffuser elements 45 on the redirecting
panel 40 which is being addressed are switched `on` to diffuse
redirected light incident upon them; the diffuser elements 45 on
the remaining redirecting panels 40 are switched `off` and are
simply then transparent optical elements, which allow the light to
pass through without further diffusion. Accordingly, redirected
light intercepts a strip of diffuser 45 only once during its
passage through the optical panels. Light which is diffused by any
particular diffuser element 45 in the array of optical panels 40
thus appears to originate from the location of that diffuser
element (rather than from infinity or any other location in the
display system). In this way, the viewer is able to perceive the
depth effect of the volumetric display system.
[0099] As will be understood, when light is diffused from an
element 45 on an optical panel 40, the light leaves the element in
a generally cone-shaped profile. Thus, when displaying the 2D
images simultaneously, diffuser elements 45 on adjacent panels are
positioned progressively further away vertically from that element,
because of the problem of early light cones hitting subsequent
diffuser elements. Simultaneous volumetric display systems are
therefore restricted in the total number of light redirecting
panels 40 which may be usefully provided. Typically, the number is
around four.
[0100] In an alternative embodiment to that shown in FIG. 7, some
of the projectors 50 are situated on the opposite side to the other
projectors 50, as opposed to all the projectors being on the same
side, as in FIG. 7.
[0101] Practically, it is relatively difficult to implement the
volumetric display system shown in FIG. 7, since aligning a large
number of optical panels 40 is not straightforward. A modification
of the embodiment of FIG. 7 is shown in FIG. 8. Here, an
emitter/modulator 60 is used to scan at high rate the respective 2D
image section for each of the plurality of optical panels 40, by
means of controlled rotating and folding mirrors, 70 and 75
respectively. The projector 60 generates a series of 2D sectional
images of the 3D image which is to be displayed. As the rotating
mirror 70 turns, the projected images are reflected, but in a
scanning action as a result of the varying angle of incidence
caused by the mirror rotation. The projector 60 therefore projects
the 2D images in scanned portions which are produced by scanning
through each 2D image from bottom to top or vice versa. The
rotating mirror is shown in FIG. 8 as having a polygonal
cross-section, but may take any appropriate form. In this
embodiment, the folding mirror 70 is shown as an octagonal
cylinder, having a length (i.e., distance from its left to right
octagonal ends) which is preferably at least the same length as the
optical panels. The projector 60 and rotating mirror 70 are
arranged so that the time taken for the projector to scan a 2D
image is equal to the time taken for the mirror to rotate through
45 degrees (1/8 of a full rotation). In this way, one rectangular
face of the rotating mirror 70 is made to reflect a single scanned
2D image from the projector 60. Each folding mirror 75 in turn
intercepts the reflected and scanned image from the rotating mirror
70, as a result of which, that scanned image is reflected from the
folding mirror and scanned over the rear surface of its respective
light-redirecting panel 40, vertically either from top to bottom or
bottom to top of the panel. For each respective 2D section of the
3D image, the next folding mirror 75 and associated panel 40
receive the image component, which is then redirected generally
perpendicularly to the front and rear surfaces of the panels 40, in
a downstream direction towards the viewing region 24. Thus the 2D
sections of the overall image are displayed sequentially (or in any
suitable repeated order) on the optical panels 40 and diffused by
diffuser elements 45 located on the front surfaces of the panels,
so that the desired depth perception may be achieved and the 3D
image may be observed.
[0102] Of course, the folding mirror 70 may have a number of sides
less than or more than eight, or may take a different form
altogether, depending on the particular application and associated
projection considerations.
[0103] However, the embodiment shown in FIG. 8 still requires the
alignment of a large number of optical panels 40 as does the
previous embodiment shown in FIG. 7. Having said that, better
resolution can be achieved with the embodiment of FIG. 8 than with
that of FIG. 7.
[0104] A further embodiment illustrating a volumetric display
system is shown in FIG. 9. Here, an optical redirecting panel 80 is
used in combination with a plurality of panel diffusers 90. The
optical panel 80 directs the light projected upon it by the
projector 50 by total internal reflection towards the viewer, as
described above. The redirected light is then diffused by the
strips of diffuser 45 that are arranged in such a way that each
panel 90 diffuses a specific section of the volumetric 3D image, as
shown in FIG. 9. The image projected on the optical panel 80 is a
combination of multiple sections of a volumetric image in such a
way that each horizontal strip of diffuser 45 will diffuse the
correct section of the 2D image. Accordingly, the viewer is able to
perceive the depth effect of the volumetric display system.
[0105] In this embodiment, the projector 50 is arranged to project
the entire 3D volumetric image at the same time, as spatially
multiplexed image lines or strips. Associated with each rib of the
redirecting panel 80 is a respective diffuser element 45 from each
respective panel diffuser 90. Thus, each rib receives from the
projector 50 a respective array of image lines, each respective one
of the image lines in the array being redirected by the rib and
diffused by a different one of its associated diffuser elements 45.
Each rib therefore is able to redirect light which is intended for
diffusion at different image depths throughout the display.
Conversely, different ribs are arranged to redirect light
(respective image lines) to different diffuser elements 45 in the
same depth plane (for example, the rearmost panel diffuser 90
receives light from the lowest and the second highest ribs in the
redirecting panel 80 shown in FIG. 9).
[0106] In practice, the number of panel diffusers 90 used in this
embodiment is around four or five, but this number may be up to 20
exceptionally.
[0107] As an alternative to simultaneous projection by the
projector 50, the projector may scan the image lines/sections.
[0108] FIG. 10 shows another 3D display system that operates in a
similar manner to that shown in FIG. 9. This display has an
automatic positioning system driven by a servo motor or some other
electronic or mechanical positioning system. The position is
controlled and synchronised with the projector 50 to propagate and
diffuse the temporally multiplexed images through a plurality of
aligned diffusing elements, which vary uniformly from panel to
panel. The optical panel 80 is vibrated or reciprocated vertically,
to form an image on the array of strips of diffuser 45 on each
panel diffuser 90 in turn. This activates each set of diffuser
strips 45 in sequence, from panel diffuser A 90, to panel diffuser
B, and then panel diffuser C, etc. Thus, the 2D image section
projected by the projector 50 is changed in synchrony with the
positional change of the redirecting panel 80, so that each panel
receives its appropriate 2D image section. The vertical distance or
pitch, d, between corresponding diffuser elements 45 on adjacent
panel diffusers 90 may be equal to the height of an individual
diffuser element. Alternatively, d may be greater than the height,
to take into account the cone-shaped diffusion profile of the
diffused redirected light. If the diffuser elements 45 are
switchable, d may be less than the height.
[0109] To avoid the alignment issue which exists with the
volumetric display systems discussed above, another embodiment is
illustrated in FIG. 11. Here, a light-redirecting optical panel 80
is used in combination with structured diffusers 105, which are
arranged in a louvred stack or sloping stacked array 100. Each
redirected ray of light propagates within the diffusers 105
arranged in the louvred stack 100 and experiences a single
diffusion when it intercepts a diffuser strip. As shown in FIG. 11,
the diffuser strips are arranged in diagonal slices. The diffusion
of light along the thickness, t, of the stack 100 allows the viewer
to perceive the depth of the 3D volumetric image. The projection
system is arranged to project the whole image simultaneously, as
with the embodiment described with reference to FIG. 9. However, in
this case, the limitation on the number of arrayed image lines per
rib (corresponding to the number of downstream panel diffusers 90)
is not such a concern, since the louvred diffuser elements 105 form
substantially continuous slices of diffuser. The projected image
lines/sections may be produced by a single projector, or by
multiple projectors. The volumetric image is formed either by
scanning different images or by projecting a single (2D) image
containing the depth information by spatially multiplexing.
[0110] The thickness, t, of the louvred stack 100 may be in the
range of 0.5 centimetres to 300 centimetres; more preferably, the
thickness, t, is in the range of 0.5 centimetres to 100
centimetres. This large range can be achieved, but increases in the
thickness are at the expense of image resolution. For this reason,
it is preferred to employ multiple projectors, which serves to
mitigate such losses in resolution.
[0111] While some of the above embodiments have been described as
comprising two redirecting optical panels for autostereoscopic
viewing, it is possible to provide only one optical panel, as shown
in FIG. 12. In this case, the panel comprises ribs, each of which
is arranged to channel both the left-eye image and the right-eye
image, from the respective projectors 18L, 18R. Providing the
projectors on opposite sides of the panel is necessary in this
particular embodiment in order to keep the left and right images
separate from each other. In this way, both sides of each rib are
used for external transmission and internal reflection of the
light. FIG. 12 illustrates this alternative, showing a single rib
from the light redirecting panel 20.
[0112] The examples given herein are presented to enable those
skilled in the art to more clearly understand and practice the
invention. The examples should not be considered as limitations
upon the scope of the invention, but as merely illustrative.
Numerous modifications and alternative embodiments of the invention
will be apparent to those skilled in the art, in view of the
foregoing description, and the following claims are intended to
cover all such modifications and variations.
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